Vespasian began building the Colosseum - which has hosted gory battles between combinations of gladiators, slaves, prisoners and wild animals of all descriptions - in AD 72 on the site of a newly drained lake in the grounds of Nero's Domus Aurea. Restoration carried out in 2001 opened up much larger areas of the arena to the public, including a reconstructed section of the sand-covered wood floor that allows visitors to walk across a platform and look down into the elevator shafts through which animals emerged, via trapdoors, into the arena. The top rows of the Colosseum are the best vantage point from which to appreciate the massive scale of the building.

Properly called the Amphitheatrum Flavium (Flavian amphitheatre), the building was later known as the Colosseum not because it was big, but because of a gold-plated colossal statue, now lost, that stood alongside. The arena was about 500 metres (a third of a mile) in circumference, could seat over 50,000 people - some scholars estimate capacity crowds numbered as many as 87,000 - and could be filled or emptied in ten minutes through a network of vomitoria (exits) that remains the basic model for stadium design today.

Nowhere in the world was there a larger or more glorious setting for mass slaughter. If costly, highly trained professional gladiators were often spared at the end of their bloody bouts, not so the slaves, criminals and assorted unfortunates roped in to do battle against them. Any combatant who disappointed the crowd by not showing enough grit was whipped until he fought more aggressively. When the combat was over, corpses were prodded with red-hot pokers to make sure no one tried to elude fate by playing dead. It was not only human life that was sacrificed to Roman blood-lust: wildlife, too, was legitimate fodder.

Animals fought animals; people fought animals. In the 100 days of carnage held to inaugurate the amphitheatre in AD 80, some 5,000 beasts perished. By the time wild-animal shows were finally banned in AD 523, the elephant and tiger were all but extinct in North Africa and Arabia. On occasion, however, the tables turned and the animals got to kill the people: a common sentence in the Roman criminal justice system was damnatio ad bestias, when thieves and other miscreants were turned loose, unarmed, into the arena, where hungry beasts would be waiting for them.

Entrance to the Colosseum was free for all, although a membership card was necessary, and a rigid seating plan kept the sexes and social classes in their rightful places. The emperor and senators occupied marble seats in the front rows; on benches higher up were the priests and magistrates, then above them the foreign diplomats. Women were confined to the upper reaches - all of them, that is, except the pampered Vestal Virgins, who had privileged seats right near the emperor.

By the sixth century, with the fall of the Roman Empire, bloodsports in the Colosseum were less impressive: chickens pecked each other to death here. The Roman authorities discontinued the games and the Colosseum became little more than a quarry for the stone and marble used to build and decorate Roman palazzi. The pockmarks all over the Colosseum's masonry date back to the ninth century, when Lombards pillaged the iron and lead clamps that until then had held the blocks together.

This irreverence toward the Colosseum was not halted until the mid 18th century, when Pope Benedict XIV consecrated it as a church. For another century it was left to its own devices, becoming home to hundreds of species of flowers and plants, as well as to a fair number of Roman homeless. After Unification in 1870 the flora was yanked up and the squatters kicked out, in what 19th-century English writer Augustus Hare described as 'aimless excavations'. 'In dragging out the roots of its shrubs,' he moaned in his Walks in Rome (1883), 'more of the building was destroyed than would have fallen naturally in five centuries.'